Abstract: The warm oil will produce thawing of ice rich soil adjacent to the pipeline when it crosses through permafrost zone, resulting in thaw settlement of the pipeline and variation of soil properties. Therefore, it is necessary for us to calculate on thawbulb growth below a warm buried pipeline for pipeline design,construction and management. According to the effect of hot
pipeline on the soil and the heat transmission of semi - infinitesoil, the paper presented a mathematical model that analyzed the thaw bulb. The characteristic equation of calculating thethaw bulb was drawn by mathematical simplification, and a satisfied solution was obtained by difference method. The method in this paper is proved feasible by a practical example.

Key words: hot oil pipeline, thermal calculation, soil, mathematical model